Over sized valves with stock carb and intake?

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Model T Ford Forum: Forum 2015: Over sized valves with stock carb and intake?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Monday, July 20, 2015 - 10:01 pm:

This 23 I am working on is running the over sized valves (intake and exhaust) with stock NH carb (this carb came off another T with no running issues)and intake. I checked for vacuum leaks, none found.
The compression is around 48 with the engine just warmed up and .020 OS pistons. The intake ports have been opened some.
For the condition and compression it's just doggie! I can't get the idle down to where it runs where it should, it has a lope to it and runs ruff somewhat at all speeds. The coils have been checked on a HCCT and are within where they should be. Newday timer in good shape with new brush. It is in proper time.
The bands are correctly adjusted, I removed the brake band because of pedal issues with Bennett pedal used for the RM brakes. I can't find a sweet spot for running speeds with the spray needle. The valves are adjusted to 12 and 14.
While the cam does not look great, I am thinking with the larger ports and valves the engine just isn't getting enough fuel/air to run correctly with the original intake/carb. The exhaust pipe and new muffler are clear, no mouse nest.
Any thoughts?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Terry Woods, Richmond, Texas on Monday, July 20, 2015 - 10:12 pm:

Mark, Before Bruce McCalley passed away, I asked him his opinion of using oversized valves in an otherwise stock engine. His answer was, definitely. Terry


Top of pagePrevious messageNext messageBottom of page Link to this message  By Eric Hylen- Central Minnesota on Monday, July 20, 2015 - 10:25 pm:

Get a Stipe .280 cam. It doesn't matter how big the valves are if the cam doesn't open them.

I built one of the top performing stock head T motors on the dyno at the 2011 MTFCI International Tour. I balanced everything, polished the ports, used 351W exhaust valves, a Stipe .280 cam with a stock head that was milled .100". It was running a Simmons carb, essentially the same an an NH.

If I recall correctly, the cars that beat it had A cranks, overheads, Z heads or some combination thereof. It out performed many cars with Z heads.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Monday, July 20, 2015 - 10:26 pm:

Running on battery or magneto?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Monday, July 20, 2015 - 10:29 pm:

Magneto but on battery runs a little worse.


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Monday, July 20, 2015 - 10:30 pm:

Sounds like cam


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Monday, July 20, 2015 - 11:12 pm:

Manifold leak perhaps? You might recheck your tappet clearance.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Richmon on Tuesday, July 21, 2015 - 06:21 am:

the only way to tell without guessing is to use a exhaust gas analyzer to check the fuel/air ratio. This will help isolate a fuel mixture problem. Also use a vacuum gauge to be sure you have enough vacuum and that it's stable at idle. Triple check you timing! You may need to find a shop with a dyno, they usually have a oxygen sensor that can be slide into the exhaust pipe to give you the mixture readings.One last thought, are you sure your cam is in proper time? Low vacuum could be an indicator of this or valve clearances being set to big. Good Luck!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Georgetown TX on Tuesday, July 21, 2015 - 06:47 am:

Low compression and idle lope seem to indicate the cam is no good or installed a tooth off maybe. The valve clearance seems too tight, that may be the issue. I would re - check cam installation and then reset the valve clearance to be sure the valves are closing all the way.

Were the valves lapped in properly? What about piston ring gap? Something is causing abnormally low compression. The size of the valves would not affect that.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Tuesday, July 21, 2015 - 11:00 am:

This is an old rebuild so don't know what gaps are on rings without tear down. Replaced the cam gear so know it's timed right. I just set the gaps on valves as needed. Took up rods. Skirt clearance is over .003. While I also think 48 ish is a bit low, don't think that I should be getting these issues. Did not grind the valves because the compression was about the same across all 4 cylinders. I also thought maybe one of the valves had too small of gap but they all were ok except a couple of intakes were more then what I would have liked so reset the gap as indicated above in my first post.
(not an update, above is where I am at now)It is running better then I first got the car to figure this all out but not out of the woods yet. I had to get it buttoned up for customer to take to car show (trailer).
RE vacuum gauge check, good idea. Never had need to try that but there is a first.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Phil Lawrence - Nevada City, CA on Tuesday, July 21, 2015 - 12:25 pm:

Mark, When you changed the cam gear did you center the timing gear cover to the camshaft?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Tuesday, July 21, 2015 - 05:42 pm:

Normally I do but because of the cork neoprene gaskets (think VERY squished!!!) used in the rest of the engine and not wanting to rely on just RTV I got it real close as in it almost just wanted to slip in but not quite.
This running issue has been with this car as long as the guy has had it. With the Newday the small amount it is off really should not affect the running. I had pulled the cover to check to see if it had been off one tooth, it hadn't but needed to replace the fiber gear as it was getting loose on the pins.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gerald Hansen on Tuesday, July 21, 2015 - 09:21 pm:

Had one with same problems, the cure replaced the weak valve springs


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Tuesday, July 21, 2015 - 11:31 pm:

RE springs, with the over sized and new style keepers the springs are under more compression then normal T. It's a thought.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd, ............Red Deer, Alberta on Wednesday, July 22, 2015 - 11:51 am:

"Sounds like cam"

Ditto


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Owens on Wednesday, July 22, 2015 - 12:15 pm:

When you change to modern springs the tension is way more that stock Ford springs and can wipe out the lobes. Maybe you can check the lift of the valve? Scott


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kenny Edmondson, Indianapolis on Wednesday, July 22, 2015 - 01:16 pm:

Sounds like a vacuum leak.


Top of pagePrevious messageNext messageBottom of page Link to this message  By jeff cordes on Wednesday, July 22, 2015 - 05:24 pm:

You might try checking the valves using the piston position method. I've seen timing gears stamped wrong from the factory.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Plank - Three Way, TN on Wednesday, July 22, 2015 - 06:14 pm:

Ditto on the timing gears stamped wrong. I pulled my hair out trying to get my engine to run after rebuilding it. I finally checked piston position relative to valve opening and discovered the new aluminum cam gear was marked one tooth off.


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